Opioids are available in different strengths and formulations. The route of administration will depend on the patient’s level of function, and the location, intensity and type of pain. All of these are important factors to consider when choosing an appropriate opioid regimen for a patient.
Common routes of administration include oral, sublingual, transdermal, transmucosal, rectal suppository, intravenous, and subcutaneous injection. Less common routes include topical, intramuscular injection (not recommended), intrathecal (spinal or epidural) and implantation.
According to the World Health Organization (WHO),1 oral administration of opioids is the preferred route of administration, owing to the simplicity, convenience and efficacy. The patient should initially be started on short-acting preparations and, once their dose has been titrated, should then be changed to a longer-acting preparation. There is less risk of addiction or breakthrough pain developing with long-acting preparations due to maintenance of more constant drug plasma levels.
Patients should be titrated up to pain control with either shorter acting preparations and then transfer to longer acting preparations when stable or be titrated using a prolonged release oral opioid with a rapid onset of action. Additional immediate release preparations should be provided throughout for rescue analgesia.
Patients taking oral therapy will obviously need to be able to swallow medication adequately and will also require a functioning gut. This is important when treating patients who undergo surgical procedures.
There are many different oral formulations, for example: solutions, sublingual tablets, suspensions, capsules and transmucosal lozenges (with integral oromucosal applicator).2 Prolonged release tablets and capsules are also available, and some prolonged release capsule preparations can be opened and the contents sprinkled over food to aid administration.2
This is a useful route of action for patients who are unable to swallow. Care should be taken that the product being used has been specifically prepared for rectal administration.
This is a useful method of administration for patients on chronic therapy who require an alternative to the oral route. Patches last for between 72 hours and 7 days, depending on the formulation2 (please refer to product literature). It is important that patients are monitored when first initiated on this treatment as it can take in excess of 24 hours for adequate plasma concentrations to be reached.2 The initial dose is generally based on a patient’s 24-hour opioid requirement, although the product literature should be consulted for dosing guidance.2 Due to the method of drug release and the long duration of action, plasma concentrations are generally steady, reducing the likelihood of adverse effects or breakthrough pain caused by fluctuating drug-plasma levels, more commonly associated with short-acting preparations.
However, in view of their long duration of action, patients who experience severe side effects should be monitored for at least 36 hours after the patch is removed (please consult product literature).2
This is a relatively pain-free method of administration, however outpatients wishing to self-administer will require special training.2
This is the quickest way to relieve pain;3 with peak plasma levels being achieved within a few minutes following administration.3 Caution should be exercised however, as peak plasma levels can become high, especially when large bolus doses are given,3 which may lead to adverse effects. If this becomes problematic, then the dose can be divided and given in a succession of smaller doses until the desired effect is achieved.3
This can be used for patients suffering persistent pain,2 but the length of regimen and dosing scheme should be taken into account as intramuscular injection can be uncomfortable, especially if large volumes are given. Also, outpatient’s wishing to self-administer will require special training. Intramuscular injection is considered a largely obsolete route of administration, and is not recommended, due to the likelihood of patient discomfort.
For most opioids, peak plasma levels are not achieved until 15 - 30 minutes after administration.3 Intramuscular bolus doses have a longer duration of action than intravenous bolus doses.3
Cancer Pain Release, a publication of the WHO, provides comprehensive guidelines discussing how best to control pain when opioids administered by mouth are ineffective. Their recommendations, highlighting the advantages and disadvantages of each route of administration, are available online at: http://www.whocancerpain.wisc.edu/eng/16_1-2/16_1-2.html
1) Cancer Pain Release - Volume 16, Nos. 1 & 2. 2003: Available from: URL: http://www.whocancerpain.wisc.edu/eng/16_1-2/16_1-2.html.
2) British National Formulary. Available from: URL: http://www.bnf.org/bnf/.
3) Pethidine and other ‘Opioid’ drugs. (2003). Royal North Shore Pain Site. Available from: URL: www.manbit.com/obstetspain/peth1.htm.